Unlike glass and aluminium, every time plastic is recycled, the polymer chain grows shorter which decreases its quality. The same piece of plastic can only be recycled about 2-3 times before it can no longer be used to make new products.
But a team of researchers at three facilities at the US Department of Energy's Lawrence Berkeley National Laboratory have developed an infinitely recyclable plastic known as poly(diketoenamine), or PDK.
"This is the first time that bioproducts have been integrated to make a PDK that is predominantly bio-based," said Brett Helms, staff scientist at the Molecular Foundry who led the project. "And it's the first time that you see a bio-advantage over using petrochemicals, both with respect to the material's properties and the cost of producing it at scale."
Unlike traditional plastics, PDK can be repeatedly deconstructed into pristine building blocks and formed into new products with no loss in quality. They are typically created from building blocks derived from petrochemicals, but those ingredients can be redesigned and produced with microbes instead.
Following a four-year study, the team has successfully manipulated E. coli to turn sugars from plants into some of the starting materials and produced a PDK with roughly 80 per cent bio-content.
"We've demonstrated that the pathway to 100 per cent bio-content in recyclable plastics is feasible," said project scientist Jeremy Demarteau. "You'll see that from us in the future."
PDKs can be used for a variety of products, including adhesives, flexible items like computer cables or watch bands, building materials, and "tough thermosets," rigid plastics made through a curing process.
The E. coli starter also had beneficial effects and allowed the material to expand its working temperature range by up to 60°C compared to the petrochemical version. This could allow it to be used in a broader array of applications such as sports gear and automotive parts including bumpers or dashboards.
The United Nations Environment Program (UNEP) estimates that we globally produce about 400 million tons of plastic waste every year, and that number is predicted to climb to more than 1 billion tons by 2050. Of the 7 billion tons of plastic waste already created, only about 10 per cent has been recycled, while most is discarded into landfills or burned.
UNEP recently said that plastic pollution could be reduced by 80 per cent by 2040 if countries and companies make policy and market shifts using existing technologies.
"We can't keep using our dwindling supply of fossil fuels to feed this insatiable desire for plastics," said Jay Keasling, a professor at UC Berkeley. "We want to help solve the plastic waste problem by creating materials that are both biorenewable and circular – and providing an incentive for companies to use them. Then people could have the products they need for the time they need them, before those items are transformed into something new."
The researchers believe that even "modest" improvements to the production process could allow bio-based PDK plastics to be made that are both cheaper and emit less CO2 than those made with fossil fuels.
